Ionic liquids 1 -butyl-3-methylimidazolium hexafluorophosphate

Michael additions of various aldehydes and ketones to 2-(/3-nittovinyl)thiophene have been carried out in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. Yields were in general better with aldehydes than with ketones. The best catalyst was L-proline <2004EJ01577>. 

Yao, Q., Zhang, Y. Olefin metathesis in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate using a recyclable Ru catalyst Remarkable effect of a designer ionic tag. Angew. Chem., Int. Ed. Engl. 2003,42, 3395-3398. 

The hetero Diels-Alder reaction of a series of functionalized 2(li-f)-pyrazinones was studied in detail by Van der Eycken et al. [58, 65]. For example, in a series of intramolecular cycioadditions of alkenyl-tethered 2(li-f)-pyrazinones 27 the reaction required 1-2 days under conventional thermal conditions (chlorobenzene, reflux, 132 °C) whereas use of 1,2-dichloroethane doped with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPFe) and use of micro-waves up to a temperature of 190 °C (sealed vessels) enabled the same transformations to be completed within 8-15 min. The primary imidoyl chloride cycloadducts were not isolated, but were rapidly hydrolyzed under the action of microwaves by addition of small amounts of water (130 °C, 5 min). The overall yields of 28 were in the same range as reported for the conventional thermal procedures (Scheme 11.8) [58]. 

Antony, J. H., Mertens, D., Dolle, A., Wasserscheid, P. and Carper, W. R., Molecular reorientational dynamics of the neat ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate by measurement of C-13 nuclear magnetic relaxation data, Chem. Phys. Chem. 4, 588-594 (2003). 

Zafarani-Moattar, M.T. Majdan-Cegincara, R. (2007). Viscosity, Density, Speed of Sound, and Refractive Index of Binary Mixtures of Organic Solvent + Ionic Liquid, 1-Butyl-3-methylimidazolium Hexafluorophosphate at 298.15 K. J.Chem. Eng. Data, 51, 6 (November 2007) 2359-2364. 

Such an example is shown on Fig. 8, which corresponds to the case of a butyl-methylimidazolium hexafluorophosphate ionic liquid (with graphite electrodes). The polynomial fits lead to differential capacitances which vary very diffently with potential from one case to another. Several peaks are observed, but their positions change markedly depending on the fit. 

Figure 4.2-1 shows the calculated ab initio molecular structure of the ionic liquid [BMIM][PFg] (l-butyl-3-methylimidazolium hexafluorophosphate). 

Lipases from C. antarctica and P. cepacia showed higher enantioselectivity in the two ionic liquids l-ethyl-3-methylimidazolium tetrafluoroborate and l-butyl-3-methylimidazolium hexafluoroborate than in THE and toluene, in the kinetic resolution of several secondary alcohols [49]. Similarly, with lipases from Pseudomonas species and Alcaligenes species, increased enantioselectivity was observed in the resolution of 1 -phenylethanol in several ionic liquids as compared to methyl tert-butyl ether [50]. Another study has demonstrated that lipase from Candida rugosa is at least 100% more selective in l-butyl-3-methylimidazolium hexafluoroborate and l-octyl-3-nonylimidazolium hexafluorophosphate than in n-hexane, in the resolution of racemic 2-chloro-propanoic acid [51]. 

Scheme 6.93) [192]. Using either of the two solvent systems, all studied cycloaddition reactions were completed in less than 1 min upon microwave irradiation at 50 °C employing 3 mol% of the catalyst. An additional advantage of using the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) as solvent is that it facilitates catalyst recycling. 

Inter- and intramolecular hetero-Diels-Alder cycloaddition reactions in a series of functionalized 2-(lH)-pyrazinones have been studied in detail by the groups of Van der Eycken and Kappe (Scheme 6.95) [195-197]. In the intramolecular series, cycloaddition of alkenyl-tethered 2-(lH)-pyrazinones required 1-2 days under conventional thermal conditions involving chlorobenzene as solvent under reflux conditions (132 °C). Switching to 1,2-dichloroethane doped with the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) and sealed-vessel microwave technology, the same transformations were completed within 8-18 min at a reaction temperature of 190 °C (Scheme 6.95 a) [195]. Without isolating the primary imidoyl chloride cycloadducts, rapid hydrolysis was achieved by the addition of small amounts of water and subjecting the reaction mixture to further microwave irradia-... 

Three ionic liquids were purchased from Aldrich l-butyl-3-methylimidazolium chloride, l-butyl-3-methylimidazolium hexafluorophosphate and l-butyl-3-methylimidazolium tetrafluoroborate. Homogeneous Co (II) catalyst precursors used in our experiments include Co(BF4)2, Co(OAc)2, and Co(C104)2 each of which have high solubilities in above ionic liquids. High surface area catalyst supports Si02 and AI2O3 were obtained from Davison and Engelhard, respectively. 

Morrow, T.l. and Maginn, E.J., Molecular dynamics study of the ionic liquid l-n-butyl-3-methylimidazolium hexafluorophosphate, ]. Phys. Chem. B, 106, 12807,2002. 

Zafarani-Moattar, M.T. and Shekaari, H. Volumetric and speed of sound of ionic liquid, l-butyl-3-methylimidazolium hexafluorophosphate with acetonitrile and methanol at T = (298.15 to 318.15) K, /. Chem., Eng. Data, 50,1694,2005. Wang, J. et al.. Excess molar volumes and excess logarithm viscosities for binary mixtures of the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate with some organic solvents, /. Solution Chem., 34, 585, 2005. 

Swatloski, R.P., Holbrey, J.D., and Rogers, R.D., Ionic liquids are not always green hydrolysis of l-butyl-3-methylimidazolium hexafluorophosphate. Green Chem., 5, 361-363, 2003. 

Planeta, J. and Roth, M., Partition coefficients of low-volatility solutes in the ionic liquid l-M-butyl-3-methylimidazolium hexafluorophosphate-supercritical CO2 system from chromatographic retention measurements,. Phys. Chem. B, 108, 11244-11249, 2004. 

Carda-Broch, S., Berthod, A., and Armstrong, D. W., Solvent properties of the l-butyl-3-methylimidazolium hexafluorophosphate ionic liquid. Anal. Bioanal. Chem., 375,191-199, 2003. 

Wang, J.-H., Cheng, D.-H., Chen, X.-W., Du, Z., Fang, Z.-L., Direct extraction of double-stranded DNA into ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate and its quantification. Anal. Chem., 79, 620-625, 2007. 

The reaction of l- -butyl-3-methylimidazolium chloride (BMIC) with sodium tet-rafluoroborate or sodium hexafluorophosphate produced the room temperature-, air-and water-stable molten salts (BMr)(BF4 ) and (BMTXPFg ), respectively in almost quantitative yield. The rhodium complexes RhCKPPhjls and (Rh(cod)2)(BF4 ) are completely soluble in these ionic liquids and they are able to catalyze the hydrogenation of cyclohexene at 10 atm and 25°C in a typical two-phase catalysis with turnovers up to 6000 (see fig. 6.10). 

This structural change is suppressed by the addition of tetrahydrothiophene (THT)19b. It prevents the formation of polymethylene zinc, i.e. (—CH2Zn—) . Without THT, a solution of 3 in THF yields polymethylene zinc at 60 °C. Monomeric bis(iodozincio)methane (3) is much more active for methylenation as compared to polymethylene zinc. As shown in Table 3 (entry 3), the addition of THT to the reaction mixture at 60 °C improved the yield of the alkene dramatically. Practically, however, its stinking property makes the experimental procedure in large scale uncomfortable. Fortunately, an ionic Uquid, l-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), plays the same role. Ionic liquid also stabilizes the monomeric structure of 3 even at 60 °C and maintains it during the reaction at the same temperature. The method can be applied to various ketones as shown in Scheme 14.4... 

The use of ionic liquids in microwave chemistry has great potential and a number of research groups have introduced the use of ionic liquids in synthetic approaches43,44. l-Butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) was recently evaluated as a solvent for the microwave-promoted Heck reaction45. Terminal arylations of electron-poor olefins were carried out rapidly with good-to-excellent yields, using the old-fashioned catalyst palladium chloride (Scheme 2.15). As an example, the... 

A further step towards optimised conditions in the catalytic transfer hydrogenation of alkenes was achieved with the introduction of the ionic liquid N-butyl-N -methylimidazolium hexafluorophosphate (BMIMPFg) as a solvent. The reduction of alkenes with formates and Pd/C in BMIMPF6 leads to saturated hydrocarbons in high yields. With an alkyne, a mixture of cis/trans alkenes and the saturated alkane was obtained (Scheme 4.5). Sufficiently pure products were isolated by a simple liquid-liquid... 

The Kotsuki group investigated the effect of high-pressure conditions on the direct proline-catalyzed aldol reaction [79a], a process which, interestingly, does not require use of DMSO as co-solvent. Use of high-pressure conditions led to suppression of the formation of undesired dehydrated by-product and enhancement of the yield. Study of the substrate range with a range of aldehydes and ketones revealed that enantioselectivity was usually comparable with that obtained from experiments at atmospheric pressure. Additionally, proline catalyzed aldol reactions in ionic liquids, preferably l-butyl-3-methylimidazolium hexafluorophosphate, have been successfully carried out [79b,c]. 

Swatloski, R. P., Holbrey, J. D., Rogers, R. D. (2003), Ionic Liquids are not always Green Hydrolysis of l-butyl-3-Methylimidazolium Hexafluorophosphate, Green Chem. 5, 361-363. 

Anthony, J. L., Maginn, E. J., Brennecke, J. F. (2002), Solubilities and Thermodynamic Properties of Gases in the Ionic Liquid l- -Butyl-3-methylimidazolium Hexafluorophosphate, J. Phys. Chem. B 106, 7315-7320. 

In 1992, Wilkes and Zaworotko described the synthesis of the first imidazolium tetra-fluoroborate ionic liquids [6], These systems together with the slightly later published [7] hexafluorophosphate analogues are the working horses of the actual research with ionic liquid. However, their use in many technical applications is still limited by their relatively high sensitivity versus hydrolysis. The tendency of anion hydrolysis is of course much less pronounced than for the chloroaluminate melts but still existent. The [PFe] anion of 1-butyl-3-methylimidazolium ([BMIM]) hexafluorophosphate - for example - has been found in our laboratories to completely hydrolyse after addition of excess water when the sample... 

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